In Part B, participants will be randomly assigned to receive study vaccine or control vaccine in one of three vaccination groups. Group 6 participants will receive the FPV vaccine pair or FPV control at each vaccine visit. Group 7 participants will receive the MVA vaccine pair or MVA control at study entry and Month 1, then a fixed dose of the FPV vaccine pair or FPV control at Months 3, 5, and 7. Group 8 participants will receive the MVA vaccine pair at MTD or MVA control at each vaccine visit. Enrollment into Groups 6, 7, and 8 will begin simultaneously after the completion of the safety data evaluation of Groups 1 and 2.